Dear [Recipient's Name], I am writing this letter to inform you that I need to cancel/reschedule the appointment that we had scheduled for [date] at [time]. I deeply apologize for any inconvenience this may cause and appreciate your understanding. I regret to inform you that due to [mention the reason for cancellation/rescheduling e.g., unexpected personal circumstances, sudden illness, an important family matter], I am unable to keep the appointment as planned. Furthermore, I understand the value of your time and apologize for any disruption caused by this change. If possible, I would like to reschedule the appointment for a more convenient time. I am available on [provide alternative dates and times that are suitable for you]. Please let me know which of these options work best for you, or if any alternative time slot is more suitable, kindly suggest an alternative time. I would be happy to accommodate your schedule. Again, I sincerely apologize for any complications this may cause and assure you that this decision was not taken lightly. I value the opportunity to meet with you and appreciate your understanding in this matter. Thank you in advance for your prompt attention to this matter, and I look forward to receiving your response. Kind regards, [Your Name] [Your Contact Information] [Date]